Preparation And Study Of Li-Storage Property Of Biomass Rice Husk-silicon Based(SiO₂,SiO_x And Si)/Carbon Composites

It has become the main direction of researchers to seek electrode materials with high energy density,low-cost and environment-friendly for lithium ion batteries(LIBs).Biomass rice husks(RHs)with silicon-rich are mainly composed of organic carbon and silicate,and are regarded as high-quality raw material for the anode of LIBs in view of the micro-nano structure of carbon and silica formed naturally during its growth.RHs-silica nanoparticles enable provide high specific capacity and organic carbon can be used to alleviate the volume expansion of electrode material during charge-discharge process,improving the cyclic stability.The unique structure and composition of RHs are full utilized to prepare desirable electrode materials,which can not only improve the electrochemical performance of electrode material for LIBs,but also realize the high-value application of agricultural waste RHs.In this paper,a variety of RHs-silicon based(SiO2,SiOx and Si)/carbon composites,derived from biomass rice husks,were designed and prepared by simple mechanical ball mill.And it was found that the chemical composition,structure and morphology of composites had an influence on its electrochemical property.The purpose of this research is to achieve high-value application of RHs and comprehensively improve the electrochemical performance of composites.The main results of this work are as follows:1.N-doped carbon/silica(SiO2/NC)composites were prepared,derived from RHs and urea,via the mechanical ball mill and N-doping process.Silica possesses the high theoretical specific capacity,and yet poor conductivity,which limits the full use of electrochemical kinetics and electrochemical performance.The doping of nitrogen into SiO2/C composite can both improve electrical conductivity of electrode material and generate the more structural defects of carbon,thus effectively enhancing the electrochemical dynamic and increasing the active sites for Li-storage.It is systematically discussed about in this chapter the effect of ball milling,urea dosage and nitrogen-doping temperature on physico-chemical properties of SiO2/NC composites.Additionally,it is found that Li-storage reaction of active silica can be transformed to the alloy-dealloy reaction of high-capacity silicon quickly,which further improves the Li-storage capacity of electrode material.2.The mechanical ball mill prior to nitrogen doping is of necessity,therefore N-doping pretreatment of RHs based SiO2/C was tried to perform in mill milling process.SiO2/NC composites with high N-doping content were controlled to prepare by using the different nitrogen sources and ball milling ways,which exhibits the excellent capacity of Li-storage at high current load.SiO2/NC composites vary with the experimental conditions in terms of N-doping content,type of nitrogen atoms and micro-mesoporous porosities.SiO2/NC composite obtained by dry mill and melamine,presents the highest N-doping content of 8.6 at%and the stable capacity of 587 mA h g^-1 at high current density of 1.0 A g^-1.3.The porous SiOx/C composites were prepared via ball milling pretreatment and molten salt ZnCl2,and the effects of ball mill and activation temperature on the physico-chemical property of composites were studied.Molten salt ZnCl2 can not only be regarded as the liquid medium to promote the reduction reaction between carbon and silica,but also can be used as activation agent to construct the hierarchical porous structure.At the optimum temperature,porous SiOx/C composite possesses the specific surface area of 583 m² g^-1 and pore volume of 0.79 cm³ g^-1.And the valence state of silicon of SiOx/C composite is reduced to+3.09.The corresponding electrode shows discharge capacity of 1927 mA h g^-1and Coulombic efficiency of 51%in the first cycle,and the stable capacity of 808 mA h g^-1 after 100 cycles.4.RH-silicon electrode materials were prepared by high energy mechanical ball mill to trigger magnesiothermic reduction reaction.When the milling time increases,the particle size of silicon tends to decrease and become uniform,and the content of SiOx on the surface of silicon increases,which influence the initial Coulombic efficiency,discharge capacity and cyclic performance of electrode material.In order to further improve cycling stability of silicon electrode material,the 3D conductive carbon(graphite)network and carbon coating structure were constructed by the mechanical ball mill and the pyrolysis of carbon successively.The as-obtained silicon/carbon composite displays the initial Coulombic efficiency of 81%and stable capacity of 1776mA h g^-1 after 100 cycles.In this paper,a variety of RHs-silicon based/carbon composites were designed and prepared in view of the unique structure and chemical composition of RHs.And the electrochemical performance of RHs based electrode materials was comprehensively improved.It is expected that it can provide a research idea for the high-value application of waste RHs.